1. Field of the Invention
This invention relates generally to light emitting devices and more particularly to side emitting light emitting diodes (LEDs).
2. Description of Related Art
FIG. 1A illustrates a conventional LED package 10. LED package 10 has a hemispherical lens 12 of a type well-known in the art. Package 10 may also have a reflector cup (not shown), in which an LED chip (not shown) resides, that reflects light emitted from the bottom and sides of the LED chip toward the observer. In other packages, other types of reflectors reflect the LED chip""s emitted light in a particular direction.
Lens 12 creates a field of illumination 14 roughly along a longitudinal package axis 16 of LED package 10. The vast majority of light emitted from an LED package 10 with a hemispherical lens 12 is emitted upwards away from LED package 10 with only a small portion emitted out from the sides of LED package 10.
FIG. 1B illustrates a known light emitting diode (LED) package 30 with a longitudinal package axis 26. LED package 30 includes an LED chip 38, a lens 32 with straight vertical sidewall 35 and a funnel-shaped top surface 37. There are two main paths in which the light will travel through package 30. The first light path P1 is desirable with the light emitted from chip 38 and traveling to surface 37 where total internal reflection (TIR) causes the light to exit through sidewall 35 at approximately 90 degrees to the longitudinal axis. The second light path P2 is light emitted from chip 38 towards sidewall 35 at an angle causing TIR or a reflection from sidewall 35 causing the light to exit package 30 at an angle not close to perpendicular to the longitudinal axis. This path is not desirable and limits the efficiency of side extracted light.
FIG. 2 illustrates the conventional LED package 10 of FIG. 1 coupled along an edge of a portion of a refractive light guide 20. LED package 10 is positioned on the edge of light guide 20 along the width of light guide 20. Light rays R1, R2, R3 emitted by LED package 10 are propagated along the length of light guide 20. FIG. 3 illustrates a plurality of conventional LED packages 10 positioned along the width of light guide 20 of FIG. 2. These conventional LED/light guide combinations are inefficient as they require a large number of LED packages 10 to illuminate the light guide and result in coupling inefficiencies due to relatively small acceptance angles. These conventional LED packages 10 must be arranged along the entire length of one side of light guide 20 to fully illuminate light guide 20.
A need exists for an LED package to couple efficiently to shallow reflectors and thin light guides. A need also exists for an LED package to allow these secondary optical elements to have relatively large illuminated areas.
Light emitting devices with side emission of light allow light guides and reflectors to have very thin profiles with large illuminated areas.
In accordance with one embodiment of the invention, a light emitting device includes a light emitting diode package. The package has a front surface and a back surface and contains a light emitting diode for emitting light at least in a first direction approximately normal to the front surface away from the package. There is also a lens extending from the front surface of the package for receiving light from the diode. The lens is shaped to redirect light received from the diode, including the light in the first direction, such that a majority of light emitted from the lens is generally parallel to the front surface of the package.
In accordance with another embodiment of the invention, a method of emitting light from a light emitting diode includes generating a light output from a light emitting diode package. The package has a front surface and a back surface and contains a light emitting diode for emitting light at least in a first direction approximately normal to the front surface away from the package. The method also includes redirecting light from the light emitting diode using a lens extending from the front surface of the package for receiving light from the diode, including the light in the first direction where the lens redirects light such that a majority of light emitted from the lens is generally parallel to the front surface of the package.
This invention will be more fully understood in light of the following detailed description taken together with the accompanying drawings.